Fluid handling systems and other fluid valve systems include a valve having a rotor. The rotor often includes a plastic disk with various ports. As the disk rotor rotates, the various ports control the flow of fluid through the valve.
Typically, an electric motor is coupled to the rotor to provide the rotational movement of the rotor. A motor control is used to control activation of the motor as required by the system. The size of the motor is dictated by several factors including the rotational load of the rotor and the breakaway torque necessary to start rotation of the rotor from a resting position. The necessary breakaway torque is dependent, in part, on the friction of the rotating surface of the disk and the eccentric actuating forces applied to the rotor during rotation which tend to lift, or cant, the rotor, causing extensive tension. It is therefore desirable to provide a disk rotor having a low friction surface.
As fluid handling systems often have a long service life, the opportunity is present for contaminants (lime, iron, rust etc.) to build up on the disk producing a rough surface which increases the coefficient of friction. The combination of the rotor ports and contaminated disk surface tend to displace and further wear the stationary rubber gaskets engaged with the rotating disk.
Various prior art systems have addressed the issue of low friction surfaces, as well as improving other properties of the component parts.
In various fluid-handling systems where high pressures and temperatures are present, there is a demand for component parts with improved pressure and heat-resistant properties. Increases in the variety of chemicals and liquids encountered in fluid-handling systems have created a greater need for corrosion-resistant component parts. One of the known methods for improving the corrosion and wear resistance of components is to cover the surface of the system components with a coating of an appropriate material.
A variety of materials have been used in the past as corrosion resistant coatings, including polytetrafluoroethylene (PTFE) and other fluorocarbon polymers. PTFE, also known under the trademark Teflon, is used in protecting and improving properties of various component units, such as liquid control valves and the components thereof. In the form of a powdered resin, PTFE can be molded in sheets and other shapes, or directly into a finished part of a product. Sheets, bars, or other shapes of compression molded PTFE are used to create many useful articles that take advantage of its chemically impervious nature and low coefficient of friction.
Valves and valve components using such material as a lining or coating have been described or suggested, as for example, in U.S. Pat. No. 3,537,700, which discloses a corrosion resistant coating formed on the base member by an isostatic compression using granular polymeric PTFE powder, then removed and heated to a temperature above the gel point of PTFE. The process is costly, and the coating is not reliable when used under pressure and high temperatures. Present methods of coating molded articles with adhesive-free polymers are also unsatisfactory. Often the bond between the coating and article surface is inconsistent, resulting in separation of the coating from the molded article.
U.S. Pat. No. 5,295,520 discloses a rotary face valve which has been used in carousel-type beverage filers. Positioned within the body is a Teflon disk which provides the dynamic sealing surface for engagement by the valve rotor. An adjustable spring provides a bias force which urges the rotor against the disk. Passages formed in the valve body and Teflon disk communicate with the various lines and nozzle and cooperate with connecting passages in the valve rotor.
U.S. Pat. No. 5,296,183 discloses a method, particularly for comolding a property enhancing coating and composite articles, which is provided by applying the coating, such as Teflon, to a formed and shaped carrier substrate which is placed into the mold. Plastic is injected into the mold such that the plastic infiltrates the irregularities in the coating surface during molding and therefore locks the coating to the part after curing.
A method for manufacturing a valve disk of a synthetic resin powder material is described in U.S. Pat. No. 4,172,112. The method includes pressure-molding two valve disk cover segments from a tetrofluoroethylene resin, molding the formed segments with a previously made disk-like core therebetween under high pressure, and then heating the valve disk segments which have been compacted and bonded integrally with the core. This method is complicated, requires expensive high pressure molding equipment, and may be effective only when a fully covered article of a complicated configuration is required.